Phenol is manufactured commercially by several processes. However one of the key manufacturing processes is air oxidation of cumene to cumene hydroperoxide (CHP) followed by acid catalyzed cleavage of this CHP to phenol and acetone. The CHP decomposition is a very exothermic reaction which is normally carried out on a commercial scale in continuous stirred or back-mixed reactors. Generally in such reactors only a small fraction of CHP is unreacted at any given time and the reaction medium consists essentially of the products of decomposition of CHP, i.e. phenol and acetone plus any solvent for example, cumene, carried in the feed stream and other materials added with CHP to the reactor. Present in the feed stream to the cleavage reactor together with unreacted cumene and CHP are generally found small amounts of dimethylbenzyl alcohol (DMBA). Additionally small amounts of acetophenone (AP) are generally found as well. While the CHP is undergoing cleavage to phenol and acetone, the DMBA is also undergoing reaction to alphamethylstyrene (AMS), a useful product since it can be readily hydrogenated back to cumene. When reacted by itself under appropriate conditions DMBA can provide high yields of AMS. However in the presence of phenol and more specifically the mixture in the cleavage reactor, i.e. primarily phenol, acetone and cumene the usual AMS yield is normally about 50 to 60 mole % of the DMBA. Main by-products are AMS dimers and various cumylphenols which generally have no or very little commercial value in the relatively impure state as found in the cleavage reactor.
Generally the cleavage reaction has had very little study in the past. U.S. Pat. No. 4,358,618 issued to Allied, has reviewed the cleavage reaction to some extent. It also notes that the DMBA in the cumene oxidation product fed to the cleavage vessel will convert to AMS and other materials. However it found that the DMBA present in the cleavage reactor will react with CHP to form dicumylperoxide (DCP) and that such cleavage reaction should be carried out at a temperature between about 50.degree. C. and about 90.degree. C. wherein the CHP concentration is lowered to between about 0.5 and about 5.0 wt. % of the composition. This reaction product is then held at that temperature in a conduit for time sufficient to produce a second mixture wherein the CHP concentration is no more than about 0.4%. This new reaction mixture is then reacted at a very high temperature, generally between about 120.degree. and about 150.degree. C. under plug-flow reaction conditions to convert at least 90% of the DCP to AMS, phenol and acetone.
In this particular work, it is noted that the common cumene oxidation product is fed to the reactor. There is no indication of any recycle materials present in the reactor or any other increase in any specific concentrations of the materials normally present in the CHP feed stream. Additionally there is no particular control of the reaction temperatures nor is there any attempt to alter the concentration of the acid catalyst in the second and third steps, particularly the third step where the DCP is converted to AMS, phenol and acetone under high temperature.
This particular set of reactions is known to be kinetically fast and is generally run at a reasonably high temperature in order to obtain the fastest reaction, including the particularly high temperature of the conversion of DCP to AMS, phenol and acetone.
The cleavage reaction has been put through a detailed study. It has now been found that it is better to slow down the CHP decomposition reaction as well as the DCP decomposition reaction in order to achieve ultimately higher yields of phenol and acetone, primarily from the increased selectivity to AMS from the DCP decomposition. As stated previously AMS is then hydrogenated to cumene. When AMS selectivity is down, AMS dimers and what is generally known as tar are prepared to a much greater extent thereby decreasing the amount of useful AMS. In particular it has been found in the initial reaction wherein CHP is decomposed into phenol and acetone and DCP is made from the reaction of CHP and DMBA that the addition of recycle acetone as well as cumene has a particularly beneficial effect. It is preferable to do this mixing of the recycle stream prior to the entrance to the cleavage reactor. Such intense mixing brings about unusually better results. The actual CHP cleavage reaction initially stated is carried out in a non-isothermal manner and preferably in a multiplicity of sequential reactors, for example a shell-in-tube reactor, generally two to five reactors, particularly three, wherein temperature is maintained over a specific range for each reactor thereby obtaining optimal CHP conversion profile and yield. This entire first reaction is controlled by a plug-flow mini-reactor wherein the measurement of temperature difference at the inlet and outlet of the mini reactor is maintained in a certain range. This mini reactor is preferably installed as a by-pass on line at the product emitted from the last sequential reactor.
Additionally it has been observed that the preferred prior art DCP decomposition to AMS, phenol and acetone conducted at the higher temperatures of 120.degree. C. to 150.degree. C. is not truly realistic in a commercial phenol manufacturing process since it is subject to wide diversions from changes in manufacturing processing parameters such as the yield of AMS with respect to time. Also seemingly insignificant changes of CHP flow rate and concentration change in cleavage product composition both individually and together negatively affect the yield of AMS. In order to better control this decomposition reaction of DCP to phenol, acetone and AMS, I have lowered the temperature range substantially as well as decreased the quantity of strong acidic catalyst present. Finally, an amine reaction product is present in an additional reactor wherein the DCP is decomposed. The total acidic materials then present are the unneutralized strong catalyst and the mild acid reaction product of the amine and the acid catalyst. The reaction product between the acidic catalyst, preferably sulfuric acid, and the amine, preferably ammonia, appears to have a co-catalytic effect in the environmental milieu although we do not wish to be bound to that observation. When only the strong catalyst is present a maximum of about 90% of the DCP in the feed can be efficiently converted to AMS before tar begins to form. But when a reduced quantity of sulfuric acid and the amine reaction product are present, over 95% of the DCP can be converted without significant loss in AMS selectivity. When sulfuric acid is reacted with ammonia the reaction product is ammonium hydrogen sulfate.
Therefore it can be thought that there are two separate invention aspects actually present here. Firstly, there is the increased yield and selectivity to CHP reaction products in the first portion of the cleavage reaction by utilizing, inter alia, additional recycle materials and a multiplicity of reactors. Secondly, the DCP prepared in the first reaction scheme of the decomposition of CHP is then selectively decomposed in an additional reactor to AMS, phenol and acetone with particular selectivity to AMS. Either of these reactions can be coupled with the known prior art synthetic procedures. It is preferred to combine both of the separate inventive steps disclosed in this particular application to form a new and highly efficient decomposition of CHP to final products of phenol, acetone and AMS.